This invention relates to a motor for rotating a magnetic disk. In particular, it relates to a motor which is used for an application in which center portions of a few magnetic disks, each normally formed with a magnetic layer on an aluminum disk, are secured to a rotor frame of the motor, and data is recorded on and reproduced from the magnetic disks by magnetic heads disposed near the upper and lower surfaces of each magnetic disk.
FIG. 4 is a longitudinal sectional view showing a conventional structure of a motor for rotating and driving a magnetic disk. In FIG. 4, an upright hollow shaft 2 is formed in the center of a circular mounting frame 1 made by aluminum die casting or the like. A motor 3 has a hollow fixed shaft 4 that is pressed onto the upright hollow shaft 2. A laminated core 6 of an armature 5 is pressed and secured to an axial central portion of the hollow fixed shaft 4. Shoulders 7 are defined on both ends of the hollow fixed shaft 4 to form small-diameter portions 8 and 9. Portion 8 is slightly longer in the axial direction than portion 9, to accommodate two Belleville springs 10 that are inserted into the small-diameter portion 8 to exert force on a roller bearing 11 that will be inserted therein, and a roller bearing 14 is pressed onto the other small-diameter portion 9 and into an end plate 13 of a rotor frame 12 so that the frame 12 may be rotatably supported on the hollow fixed shaft 4. The rotor frame 12 is in the shape of a cup. An axial cylindrical side wall 54 covers an outer peripheral surface of the armature 5, an outer end of which serves as a magnetic disk support 15 bent outwardly perpendicularly and is opposed to the mounting frame 1 leaving a small clearance. An annular recess 16 formed at an inner corner of the magnetic disk support 15 is provided for a good contact between the magnetic disk support 15 and a magnetic disk placed thereon.
An annular permanent magnet 17 having the desired number of poles is pressed and secured into the cylindrical side wall 54, after which an end plate 19 is pressed and secured to the roller bearing 11. The roller bearing 11 is then pressed and secured to shaft 2, and the end plate 19 is attached to the end of the side wall 14 to form a rotor 20. The rotor 20, the armature 6 and the hollow fixed shaft 4 comprise the motor 3. A set of lead wires 22 of an armature coil 21 is drawn out of a hole 23 provided in the hollow fixed shaft 4 into a hollow portion and pulled outside through the hollow portion of the hollow shaft 2.
FIG. 5 is a sectional view of a portion of the conventional magnetic disk driving motor having the structure described above. In FIG. 5, center holes of the magnetic disks 24 are fitted on the side wall 54 of the rotor frame 12, placed on the disk receiving base 15 in a predetermined spaced relation through spacers 25, and fixed by means of a pressure plate 26 and a screw 27. In order to maintain a predetermined small clearance between the surface of each magnetic disk 24 and a radially moving magnetic head 28, vibrations resulting from rotation of the side wall 54 and magnetic external disk support 15 have to be minimized; further, the width of vertical variation of the rotating disk support 15 should be 0.005 mm or less.
However, in the aforementioned conventional construction, it is very difficult to make the lateral hole 23 through which the lead wire 22 passes in the hollow fixed shaft 4, and the number of parts is large, which increases the cost of the motor.